Chronic stress leading gut microbiota dysbiosis and neuroinflammation promoted depressive disorder

Abstract Chronic stress was known to contribute to gut microbiota dysbiosis and central neuroinflammation, yet the underlying mechanisms remain poorly understood. In this study, forty-eight male C57BL/6 mice were randomly assigned to three groups: control, chronic unpredictable mild stress (CUMS), and CUMS with probiotic intervention. Mice in the CUMS group were exposed to four weeks of unpredictable stressors, while those in the probiotic group received oral administration of Bifidobacterium triple viable capsules during the stress period. Behavioral assessments revealed pronounced depression-like behaviors in CUMS mice, which were significantly ameliorated by probiotic treatment. 16S rRNA sequencing demonstrated that CUMS reduced gut microbial α-diversity, altered β-diversity, elevated the Firmicutes/Bacteroidetes ratio, and decreased beneficial genera such as Bifidobacterium and Lactobacillus, while increasing the abundance of Escherichia. Probiotic supplementation effectively restored these microbial alterations to near-control levels. Intestinal barrier function was compromised in CUMS mice, as indicated by reduced proteins ZO-1 and Occludin, which partially reversed by probiotic treatment. In the hippocampus and prefrontal cortex, CUMS increased the levels of pro-inflammatory cytokines (IL-1β, TNF-α, and IL-6), and upregulated microglial activation markers (Iba-1, iNOS, and COX-2) in the hippocampus. Probiotic intervention markedly suppressed these neuroinflammatory responses. Moreover, hippocampal CA1 neurons in CUMS mice exhibited structural disorganization, neuronal loss, and nuclear pyknosis, all of which were alleviated by probiotic administration. Collectively, these findings suggest that chronic stress disrupts the gut microbiota–gut–brain axis via microbial dysbiosis and intestinal barrier impairment, thereby promoting neuroinflammation and behavioral abnormalities.